#include <signal.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <string.h>
#include <arpa/inet.h>
#include <fcntl.h>
 
typedef struct sockaddr SA;
 
#define BUFFSIZE 512
int sockfd = 0;						 //定义全局的sockfd
 
//信号处理
void do_sigio(int signo) {
	char buff[512] = {0};
	struct sockaddr_in cli_addr;
	socklen_t clilen = sizeof(cli_addr);
	int rlen = recvfrom(sockfd, buff, 512, 0,
		(SA*)&cli_addr, &clilen);		//获取cli_addr, 为后面send做准备
 
	printf("Recvfrom message: %s\n", buff);
	int slen = sendto(sockfd, buff, rlen, 0, (SA*)&cli_addr, clilen);
}
 
 
int main() {
	sockfd = socket(AF_INET, SOCK_DGRAM, 0);
	if (-1 == sockfd) {
		perror("socket");
		return 2;
	} 
	signal(SIGIO, do_sigio);//注册信号处理函数
 
	//确定协议地址簇
	struct sockaddr_in serv_addr; 
	memset(&serv_addr,  0, sizeof(serv_addr));
	serv_addr.sin_family = AF_INET;
	serv_addr.sin_port = htons(8080);
	serv_addr.sin_addr.s_addr = INADDR_ANY;
 
	//设置套接口属主
	fcntl(sockfd, __F_SETOWN, getpid());
 
	//然后设置O_ASYNC 开启信号驱动IO
	int flags = fcntl(sockfd, F_GETFL);
	if (-1 == fcntl(sockfd, F_SETFL, flags | O_NONBLOCK | O_ASYNC)) {
		return 4;
	}
  
	if (-1 == bind(sockfd, (SA*)&serv_addr, sizeof(serv_addr))) {
		return 3;
	}
 
	while (1) sleep(1);
	close(sockfd);
	
	return 0;
}